Method for initiating in situ combustion within a subterranean formation



Apnl 23, 196s B. G. HOLMES 3,379,254

METHOD FOR INITIATING 1N SITU COMBUSTION WITHIN A SUBTERRANEAN FORMATION Filed Aug. 25, 1966 BILLY G. HOLMES Ywzjuewf ATTORNEY United States Patent O 3,379,254 METHOD FOR INITIATING IN SITU COMBUSTION WITHIN A SUBTERRANEAN FORMATION Billy G. Holmes, Lancaster, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Aug. 25, 1966, Ser. No. 574,963 3 Claims. (Cl. 166-38) This invention relates to recovering petroleum from a subterranean formation with in situ combustion procedures. More particularly, this invention relates to a method for initiating such in situ combustion procedures.

Petroleum recovery from subterranean formations with in situ combustion procedures is well known. Usually these procedures are employed where the petroleum is viscous. The in situ combustion procedures require the initiating of combustion by igniting the carbonaceous material within a formation, usually adjacent a well. It has been proposed to introduce into the formation readily combustible materials and then an oxidizing medium for their auto-oxidation at a rate sucient to produce spontaneous combustion. Usually, this auto-oxidation begins at formation-temperature and continues until temperatures above about 700 F. are reached before these materials ignite.

Auto-oxidation as a means for initiating in situ combustion within a formation is subject to several difficulties. The ow of the oxidizing medium requires careful regulation for auto-oxidation to generate sufficient heat to raise the temperature sufficiently of the oxidizable material that it will ignite. Experience in the field has shown that this method of ignition is not certain. Too low a rate of ow of the oxidizing medium produces insufficient heat to produce spontaneous ignition. An excessive ow of the oxidizing medium quenches the auto-oxidation reaction and prevents spontaneous combustion. Thus, ignition by the known auto-oxidation procedures is uncertain as a method for initiating in situ combustion within a formation.

Another difficulty with employing auto-oxidation is the danger of downhole explosions occurring by contact of the oxidizing medium with the readily oxidized material within the well. For example, it has been proposed to introduce linseed oil into a well and then displace it into the formation with air. Under certain conditions within the well, the linseed oil becomes sufficiently dispersed that upon contact with air spontaneous combustion occurs with explosive violence. The resulting explosion can destroy the well and cause possible injury to field personnel.

Another difficulty with auto-oxidation is the creation of a combustion front in the formation spaced from the well. This front returns to the well and, with its attendant high temperatures, causes thermal destruction of the well. For example, if linseed oil is injected into the formation adjacent a well and air subsequently is introduced from the well into the formation, the linseed oil is forced back away from the face of the formation to be disposed through the formation some distance from the well. The subsequent flow of air through the formation can then raise the temperature of the linseed oil, by auto-oxidation, sufficiently to result in its auto-ignition. The continued ow of air moves the combustion front radially through the formation, back to the well. The combustion front may also expand away from the well, but the expanding combustion front causes the injury to the well apparatus ice by creating high temperatures at the well in the formation.

The present invention has as its principal object to provide a method for initiating in situ combustion within a formation. Another object is to provide such a method without aforementioned difficulties wherein linseed oil is employed as the readily oxidizable material. Another object is to provide a method, in accordance with the foregoing objects, that: (a) produces certain ignition of the linseed oil to initiate in situ combustion within a formation; (b) is safe to employ without danger of explosions in a well; and (c) produces a combustion front upon ignition which moves through the formation only radially outwardly away from the well through which the various uids are injected into the formation.

In accordance with this invention for achieving the above-stated objects, there is provided a method in which in situ combustion is initiated in a petroleum-bearing subterranean formation penetrated -by a well. Various steps are practiced through this well in a certain manner that the formation about the well is heated to a predetermined minimum temperature with steam. Thereafter, linseed oil is introduced into the well to be disposed by a regulated flow of steam along the surface of the formation surrounding the well. Then while steam yet ows, a gaseous stream containing oxygen is injected through the well into the formation to produce immediate, spontaneous ignition of the linseed oil in the formation facing the well. Such ignition is safe and instantaneous, and results in a combustion front supported by carbonaceous materials in the formation moving radially outwardly through the formation in a direction away from the well.

Reference may be taken to the drawing wherein is shown, in a vertical section taken through the earth, a well penetrating a petroleum-containing subterranean formation wherein in situ combustion is to be initiated, and the well embodying suitable apparatus which may be employed in carrying out the steps of this invention.

The drawing shows a permeable and petroleum-containing subterranean formation 10 which resides below an overburden 12 and a superimposed strata 13. A strata 14 resides below the formation 10. The strata 13 and 14 for purposes of this invention will be considered not to contain petroleum. A well 16 extends downwardly from' the earths surface 17 and terminates adjacent the strata 14.

The well 16 may be provided with suitable apparatus for the conveying of uids between the earths surface 17 and the formation 10. For this purpose, the well 16 has a casing 18 extending downwardly from a wellhead 19 to terminate adjacent the formation 10. The casing 18 is sealed to the overburden 12 and strata 13 by a cement sheath 21. The well 16 is open-completed at the exposed face 11 of the formation 10. The well 16 carries conduit means for conveying fluids between the earths surface 17 and the formation 10. The conduit means may take the form of conduits 22 and 23. The conduit 22 extends downwardly through the wellhead 19 to terminate within the well 16 adjacent the formation 10. The conduit 23 passes through the wellhead 19 into iiuid communication with the annulus formed between the casing 18 and the conduit 22 of the well 16. This arrangement provides for two separate means for conveying fluids into the well 16 from the earths surface 17. Other arrangements may q be used as will be obvious from this description. The conduit 22 has inlets 24 and 26 through which tiow is reg- 3 l ulated, respectively, by valves 27 and 28. The conduit 23 carries a valve 29 by which to regulate the ow of uids therethrough.

lThe conduit 24 connects -to a source of steam (not shown). Various types of steam boilers and generators presently employed in the oil patch `may be used as sources of steam, if desired. The steam source needs to provide a ow of steam at suitablerconditions of tempera-ture and pressure to heat the face 11 of the formation to at least 300y F. For example, in one field test,-

pressurized steam of 80 percent quality, entering the well 16 at 550 F. fora three-hour interval was sufficient to raise the temperature of the face 1=1 of the formation 10 about the well 16 to this temperature.

The inlet 26 connects to ya supply of linseed oil (not shown). This source may be vany reservoir from which the linseed oil flows into the conduit 26. Thus, the adjustmen-t of the va-lves 27 and 2S regulates the tlow of steam and linseed oil via the conduit 22 into the well 16.

The conduit 23 connects to a source of pressurized air (not shown). The nature of the source is uncritical. A suitable supply of air was provided by an air compressor which delivered air into the conduit 23 at a rate of about 1 million standard cubic feet per day. l

han embodiment of the method of this invention will now be described relative to the use of the illustrative apparatus shown in the drawing for initiating7 in situ combustion within the formation 10. As one step, steam from a suitable source is passed via the inlet 24 into the well I16 through the conduit 22. The ow of steam is regulated with the valve 27. If desired, the steam can be introduced through the conduit 23, or other conduit means, into the well .16. The steam is introduced, under suitable conditions of temperature and pressure, that its passage into the formation 10 provides for heating the face 111 exposed to the -well 16 to a temperature of at least 300 F.

Preferably, the steam is injected at temperatures of :about 550 F. so as to introduce suitable heat energy in a short time-period into the well 16. It will be obvious that under the varied conditions permissible for injecting steam into the formation 10, the amount of time required to heat the face 11 to the desired temperature will be varied. However, the desired .temperature is for practical purposes obtained by the injection of steam under suitable conditions of pressure and temperature that 50 million B.t.u. of heat energy are introduced into the well 16 within a period of less than 18 hours. Inasmuch as the heat content of the steam is dependent upon the steam quality, it is preferred that the steam be of as high a quality as conveniently obtainable adjacent the well 16. Usually, a steam generator will easily produce a steam quality of 80 percent or better at the necessary temperatures and pressures. If desired, additives for preventing corrosion within the well, Water treatment chemicals, Iand the like, can be added to the injected steam.

During steam injection into the well 16, the valves 28 and 29 in the conduits 22 (at inlet 26) and 23, respectively, are adjusted to restrict the ow of oxygen-containing gases into the well 16. If desired, the valve 29 may be opened for a short interval during the injection of steam into the well 16 to permit any air within the well 16 to escape to the atmosphere. As a result, all gases are displaced from the well 1'6 into the formation 10, or vented to the atmosphere through available conduit means, during the steam injection step. Therefore, the steam injection into the well 16 heats the formation 10 to the desired temperature while providing an inert atmosphere within the well 16. The inert atmosphere is of great advantage in preventing explosions of subsequently introduced combustible materials into the well 16.

When the exposed face 11 of the formation 10 reaches a temperature of at least 300 F., the injection of steam is completed.

The step of injecting steam has additional beneiicial effects upon the formation 10. For example, petroleum is displaced from the face 1'1 and will not dilute the linseed oil later injected into the well 16. Also, the injectivity of subsequently introduced uids is enhanced by cleaning of the formation 10 at the well 16, and stratification of such fluids is greatly reduced. Y

The flow of stream into the inlet 24 now is interrupted by closing the valve 27, or by any other suitable means. Preferably, the valves 27, 28, and 29 are also adjusted yt0 restrict the flows of any oxygen-containing gases into the well 16. Under these conditions after steam injection, the Well 16 is sealed and-remains heated land pressurized for carrying out4 the following stepy of the present invention.

A quantity of linseed oil suficient to Wet the exposed face 11 of the formation 10 is introduced into the well i16 through one of the conduit means. Forpurposes of description, the linseed oil is introduced under suitable pressure through the inlet 26 of the'conduit 22 into the well 16. The tow of linseed oil in the conduit 22 can be regulated by the valve 28. The amount of linseed oil need only be sufliciently large to Wetthe face 11 of the formation 10. In one instance, it was found that about one gallon of linseed oil for each square foot of the face 11 was sufficient to wet properly the form-ation 10. It will he apparent that excessive quantities of linseed oil ,are not required; especially such large amounts that the pern meability to gas ows is reduced in the formation 10. It will be obvious that a relatively small amount of linseed oil needs to be employed since upon its ignition the resultant combustion front will immediately pass into, and Ibe supported by, the car-bonaceous materials present in the formation 10. Carbonaceous materials remain in the ,formation 10 after the injection of steam. However, it

will be desired in some instances to introduce additional combustiblesl into the formation 10. For example, the connate petroleum may leave only small amounts of residuary carbonaceous materials adjacent the well 16 in the formation 10.

The term linseed oil, as it is used in the present de scription of this invention, includes the various materials and products derived from the fluidextracts of axseed. Specifically included in this term are raw linseed oil;

' boiled linseed oil which may include various oxidation accelerators; and the fatty acid extracts derived directly from linseed oil or thereafter altered by various conversions. The linseed oil may be mixed with any substance which does not significantly interfere with it-s ready spontaneous ignition in the face 11.

After introducing linseed oil into the conduit 22, another step of the present invention is practiced. Steam is passed through the conduit means through which linseed oil was introduced into the well 16. In this illustrative embodiment, steam is flowed through the inlet 24 to displace the linseed oil from the lower extremity of the conduit 22 into the face 111 of the formation 10. The ow of steam should be in an amount suticient only to displace the linseed oil from the conduit 22 into -the face 111 of the formation 10. This tiow of steam must not beof such large magnitude as to drive the linseed oil from the face 11 into the formation 10 to a location some distance from the well 16. It will be apparent that only a small flow of steam is required for this purpose. While this ow of steam continues into the Well 16, the following step is practiced.

A gaseous stream containing free oxygen is injected through other of the conduit means which have not carried the linseed oil into the well 16. In this embodiment, the gaseous stream is injected through theA conduit 23 with its flow into the well 16 being regulatable by the valve 29. The gaseous stream usually will be air. However, other gases rnay be employed which contain free oxygen. The gaseous stream is injected with sufficient pressure to be forced to ow from the well 16 into the formation 10. The flow of the gaseous stream is in an amount sutlicient to support combustion of the linseed oil which Wets the face 11 of the formation 10. Since the linseed oil ignites immediately with this amount of free-oxygen carrying gaseous stream, greater amounts of ow are beneficial and cannot easily quench the resulting combustion front. It has been found that the ilow of the gaseous stream in rates of about 1.5 million cubic feet per day produces desirable results.

The gaseous stream flows from the well 16 radially outwardly into the formation an-d the free oxygen which it contains reacts immediately with the linseed oil in the preheated face 11 to produce by spontaneous ignition a combustion front along such face 11 about the well 16, This spontaneous ignition of the linseed oil obviously produces a combustion front which with the continued injection of the gaseous stream moves only radially outwardly from the well 16 through the formation 10. It will be apparent that this result is obtained because the combustion front is created initially only on the face 11 of the formation 10 about the well 16. Thereafter, this combustion front can move only outwardly through the formation 10.

The outwardly moving unidirectional combustion front resulting from ignition of the linseed oil only at the face 11 prevents damage to the well 16 from the high temperatures which in the past occurred where a combustible material was ignited initially in the formation 10 at a location some distance from the well 16. Under these lastmentioned circumstances, a combustion front would expand in the formation 10 countercurrently to the injected gaseous stream and thereby subject the well 16 to destructively high temperatures.

As another step, steam is continually passed through the conduit 22 into the well 16 until the amounts of 1inseed oil remaining in the conduit 22 are incapable of forming explosive vapors while injection of the gaseous stream into the well 16 is being undertaken. This prevents mixing of free oxygen with any residuary linseed oil under conditions within the well 16 Where hazardous and destructive explosions could occur.

The preceding steps -have now established a combustion front in the formation 10 moving away from the Well 16. At this time other steps to conduct petroleum recovery by in situ combustion procedures may be practiced.

Laboratory experiments were conducted employing a sand pack into which a quantity of petroleum was added to simulate a permeable petroleum-containing subterranean formation. The sand pack was enclosed within a pressure vessel and provided with means for recording temperatures therewithin. The sand pack was heated by a ow of steam to Various temperatures. The ow of steam at such temperatures was then interruped and a small quantity of linseed oil was added to wet the upstream face of the sand pack. A stream of air was passed through the sand pack immediately after introduction of the linseed oil. It was found from these tests that when the sand pack face presented toward the inlet of the seal was heated to at least 300 F., immediate spontaneous ignition of the linseed oil occurred and produced a combustion front which readily passed downstream into the sand pack. The conclusion from these tests was inescapable that linseed oil consistently is spontaneously ignited within a formation heated to temperatures of at least 300 F. Temperatures higher than 300 F. can be employed, if desired, at increasing heating costs.

The method of this invention was used successfully in the field to initiate in situ combustion in an oil reservoir. An injection well was equipped with a high temperature wellhead and valves in iiuid connection with a string of open-ended tubing set to the top of the formation to be ignited. This formation resided at a depth of 1,146 feet below the earths surface and had a gross interval of approximately 74 feet opened into the well. Air injection showed that the formation was permeable.

Steam of percent quality was injected through the well into the formation. At the injection pressure, the stea-m had a temperature of 550 F. The steam, equivalent to 86 barrels of water, was injected within a threehour interval. The injected steam amounted to a total heat input of about 30 million B.t.u. and heated the formation to the desired temperature.

Steam injection was terminated. A mixture of 55 gallons of boiled linseed oil with gallons of raw linseed oil was pumped into the tubing and displaced into the formation with a reduced rate of steam injection. While steam injection continued, air was introduced at a rate of about 1 million standard cubic feet per day into the casing annulus of the well.

These steps resulted in the immediate spontaneous ignition of the linseed oil to produce a combustion front which then moved outwardly into the formation and away from the wellbore. A short time thereafter, combustion gases appeared in the produced gas stream from an adjacent well to indicate the in situ combustion procedure was operative.

From the foregoing it will be apparent that there has been described a method for initiating in situ combustion within a permeable petroleum-containing subterranean formation and that this method achieves all of the stated objects of this invention by providing safe and certain initiation of in situ combustion in the formation with the resulting combustion front moving unidirectionally outwardly from the injection well through the adjacent formation.

It is intended that the foregoing description of this invention is taken by way of illustration. Various alterations in the described steps may be made by those skilled in the art without departing from the spirit of the invention. In this regard, it is intended that the limitations to the method of this invention are to be found only in the appended claims.

What is claimed is:

1. A method for initiating in situ combustion within a permeable petroleum-containing subterranean formation penetrated by an injection well having at least two conduit means for conveying fluids from the earths surface to said formation to be ignited, the steps compris- (a) injecting steam through one of said conduit means into said formation to be ignited, said steam being at suitable conditions of temperature and pressure to heat the well-exposed face of said formation to at least 300 F., and during at least terminal steam injection said conduit means being restricted to flows of oxygen-containing gas into the well;

(b) introducing into one of said conduit means a quantity of linseed oil suicient to wet the face of the formation to be ignited while interrupting the flow of other uids into the formation through said conduit means;

(c) passing steam through said conduit means receiving linseed oil in a ow suiiicient only to displace the linseed oil into the face of said formation but not to drive said linseed oil into the formation away from the well, and while the steam yet ows into the well;

(d) injecting a gaseous stream containing free oxygen through other of said conduit means which have not carried linseed oil into the formation in an amount sucient to support combustion whereby the linseed oil spontaneously ignites at the heated face of the formation and the resulting combustion front thereby moves only radially outwardly from the well into the formation; and

(e) continuing the passage of steam through said conduit means until residuary linseed oil therein is removed to an amount incapable of forming explosive vapors during the time injection of the gaseous stream is undertaken.

2. The method of claim 1 wherein the steam in step (a) is injected in an amount to provide about 50 million B.t.u. to the Well within a period of less than 18 hours.

3. The method of claim 1 wherein the gaseous stream is air injected at a rate up to about 1.5 million cubic feet of air per day.

Waller 166-11 Tadema 166-38 Herzog 166-39 Willman 166-11 Simm 166-11 X Bednarski et al 166-11 STEPHEN I. NOVOSAD, Pri/nary Examiner.

` Edward M. Fletcher, Jr.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,379,254 April Z3, 1968 Billy G. Holmes It is certified that error appears in 'the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 7, "stream" should read steam Column 5, line 66, "increasing" should read increased u Column 6 line Sl, "gas" should read gases x Signed and sealed this 2nd day of September L1969.

(SEAL) Attest:

WILLIAM E. SCHUYLE-R, JR.

Attesting Officer Commissioner of Patients 

1. A METHOD FOR INITIATING IN SITU COMBUSTION WITHIN A PERMEABLE PETROLEUM-CONTAINING SUBTERANEAN FORMATION PENETRATED BY AN NJECTION WELL HAVING AT LEAST TWO CONDUIT MEANS FOR CONVEYING FLUIDS FROM THE EARTH''S SURFACE TO SAID FORMATION TO BE IGNITED, THE STEPS COMPRISING: (A) INJECTING STEAM THROUGH ONE OF SAID CONDUIT MEANS INTO SAID FORMATION TO BE IGNITED, SAID STEAM BEING AT SUITABLE CONDITONS OF TEMPERATURE AND PRESSURE TO HEAT THE WELL-EXPOSED FACE OF SAID FORMATION TO AT LEAST 300*F., AND DURING AT LEAST TERMINAL STEAM INJECTION SAID CONDUIT MEANS BEING RESTRICTED TO FLOWS OF OXYGEN-CONTAINING GAS INTO THE WELL; (B) INTRODUCING INTO ONE OF SAID CONDUIT MEANS A QUANTITY OF LINSEED OL SUFFICIENT TO WET THE FACE OF THE FORMATION TO BE IGNITED WHILE INTERRUPTING THE FLOW OF OTHER FLUIDS INTO THE FORMATION THROUGH SAID CONDUIT MEANS; (C) PASSING STEAM THROUGH SAID CONDUIT MEANS RECEIVING LINSEED OIL IN A FLOW SUFFICIENT ONLY TO DISPLACE THE LINSEED OIL INTO THE FACE OF SAID FORMATION BUT NOT TO DRIVE SAID LINSEED OIL INTO THE FORMATION AWAY FROM THE WELL, AND WHILE THE STEAM YET FLOWS INTO THE WELL; (D) INJECTING A GASEOUS STREAM CONTAINING FREE OXYGEN THROUGH OTHER OF SAID CONDUIT MEANS WHICH HAVE NOT CARRIED LINSEED OIL INTO THE FORMATIONIN AN AMOUNT SUFFICIENT TO SUPPORT COMBUSION WHEREBY THE LINSEED OIL SPONTANEOUSLY IGNITES AT THE HEATED FACE OF THE FORMATION AND THE RESULTING COMBUSTION FRONT THEREBY MOVES ONLY RADIALLY OUTWARDLY FROM THE WELL INTO THE FORMATION; AND 